1. Field of the Invention
The present invention is related to keyboard apparatus of the type employed with digital electronic equipment. More particularly, the present invention keyboard is adapted for use in any environment in which static electricity or sparks would present a data error or environmental problem.
2. Description of the Prior Art
Many electro-magnetic devices now in use employ optical sensing devices to detect mechanical motion. Such devices are commonly known and are commercially available as sensing devices and do not require further description herein.
Touching or depressing a key on a prior art electrical keyboard results in a switch effect which either completes an electrical circuit or provides a change which can be sensed by an electrical circuit.
Electrical keyboards may be provided with physical contact electrical switches. Such switches include not only moveable contact pairs, but also include crosswires and membrane conductive contacts which physically touch to complete an electrical circuit. Switches which sense a change in capacitance and/or a change in resistance have been generally classified with electrical switches. Electrical switches may initiate or cut off the flow of electricity in the circuit being actuated. Electrical switches of all types are subject to creation of data errors when employed in a digital data keyboard because static electricity, which builds up on the human body or equipment, is sufficient to generate a flow of electricity in the sensing circuit of the electrical keyboards.
Magnetic keyboard switches of the type which do not have contact elements, operate on the Hall effect principle or a change of conductive reactance which is great enough to be sensed in an electrical circuit. Magnetic keyboard switches are also subject to errors due to electro-magnetic interference (EMI), including static electricity, which induces the flow of electricity in the sensing circuits.
Presently, keyboards are used in conjunction with medical monitering equipment, thus, extreme care should be taken to avoid all shock hazards which could be caused by ground currents and/or static discharge.
It would be desirable to eliminate the problems associated with electro-magnetic interference associated with keyboards. Not only could the digital data type of errors be eliminated, but completely passive keyboards would be desirable for use in a chemical or gas environment which could be hazardous to humans or destructive to ordinary electrical circuits and electronic components.